Computed tomography is an imaging technique that has been widely used in the medical field. In a procedure for computed tomography, an x-ray source and a detector apparatus are positioned on opposite sides of a portion of a patient under examination. The x-ray source generates and directs an x-ray beam towards the patient, while the detector apparatus measures the x-ray intensity at a plurality of transmission paths defined by the x-ray beam during the process. The detector apparatus produces a voltage proportional to the intensity of incident x-rays, and the voltage is read and digitized for subsequent processing in a computer. Based on this intensity map, the attenuation is calculated for each transmission path. By taking a large number of readings from multiple angles around the patient, relatively massive amounts of data are thus accumulated. The accumulated data are then analyzed and processed for reconstruction of a matrix (visual or otherwise), which constitutes a depiction of a density function of the bodily section being examined. By considering one or more of such sections, a skilled diagnostician can often diagnose various bodily ailments such as tumors, blood clots, etc.
When processing projection images for reconstruction of a volumetric image, image filtering may be applied for removal of noise. In existing techniques, a pre-scan gantry range (e.g. 180°) is needed to obtain parameters (e.g., fixed information) for determining a suitable filtering model. The projection images are then obtained, and the filtering model is applied to the projection images in a retrospective image reconstruction process. Such technique results in a lengthy time needed to get projection images and a considerable reconstruction delay. Techniques that use a-priori fixed filtering parameters are less flexible and may lead to inaccuracy in filtering because the resulting filter is applied to all situations the same way. Also, due to the fixed nature of the filtering model, the technique is not the most efficient.